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A laminate for use in a printed circuit board is provided. The laminate
comprises a conductive layer and a film that is positioned adjacent to
the conductive layer. The film contains a thermoset polymer formed by
reacting an aromatic polyester with a crosslinking agent that includes a
maleimide compound. The aromatic polyester includes repeating units
derived from an aromatic hydroxycarboxylic acid, aromatic
dicarboxycarboxylic acid, aromatic diol, aromatic amide, aromatic amine,
or a combination thereof.

1. A laminate comprising: a conductive layer that contains copper; a film
that is positioned adjacent to the conductive layer, wherein the film
contains a thermoset polymer formed by reacting an aromatic polyester
with a crosslinking agent that includes a maleimide compound, and further
wherein the aromatic polyester includes repeating units derived from an
aromatic hydroxycarboxylic acid, aromatic dicarboxycarboxylic acid,
aromatic diol, aromatic amide, aromatic amine, or a combination thereof.

7. The laminate of claim 1, wherein the aromatic polyester contains
repeating units derived from 6-hydroxy-2-naphthoic acid in an amount from
about 15 mol. % to about 60 mol. %, repeating units derived from
4-hydroxybenzoic acid in an amount from about 20 mol. % to about 65 mol.
%, and repeating units derived from hydroquinone and/or 4,4'-biphenol in
an amount from about 1 mol. % to about 40 mol. %.

8. The laminate of claim 1, wherein the polyester is wholly aromatic.

9. The laminate of claim 1, wherein the crosslinking agent is a
bismaleimide having the following general formula: ##STR00006## wherein
R.sup.1 is a substituted or unsubstituted, alkyl, alkenyl, alkynyl,
cycloalkyl, aryl, heteroaryl, heterocyclyl, or a combination thereof.

10. The laminate of claim 9, wherein R.sup.1 is an aryl that contains one
or more aromatic rings having from 6 to 15 carbon atoms.

[0001] The present application claims priority to U.S. Provisional
Application Ser. No. 62/310,902, filed on Mar. 21, 2016, which is
incorporated herein in its entirety by reference thereto.

BACKGROUND OF THE INVENTION

[0002] Flexible printed circuit boards are increasingly being used in high
density, small electronic components. Such circuit boards are typically
produced from a "copper clad laminate" that contains an insulating film
and a copper foil from which the circuit paths are etched. Conventional
insulating films are typically formed from polyimides due their high
degree of heat resistance. Unfortunately, however, polyimides tend to
readily absorb moisture during use, which is problematic in electronic
applications. In this regard, liquid crystalline polyesters have also
been suggested for use in forming the insulating film. Nevertheless, one
of the problems in successfully incorporating these types of polymers
into flexible printed circuit boards is that films formed from liquid
crystalline polyesters tend to lack good adhesion to copper foils. As
such, a need currently exists for a film that can be more readily formed
from high performance polymers and that can also exhibit better adhesion
to metal components.

SUMMARY OF THE INVENTION

[0003] In accordance with one embodiment of the present invention, a
laminate for use in a printed circuit board is disclosed. The laminate
comprises a conductive layer that contains copper, and a film that is
positioned adjacent to the conductive layer. The film contains a
thermoset polymer formed by reacting an aromatic polyester with a
crosslinking agent that includes a maleimide compound. The aromatic
polyester includes repeating units derived from an aromatic
hydroxycarboxylic acid, aromatic dicarboxycarboxylic acid, aromatic diol,
aromatic amide, aromatic amine, or a combination thereof.

[0004] Other features and aspects of the present invention are set forth
in greater detail below.

BRIEF DESCRIPTION OF THE FIGURES

[0005] A full and enabling disclosure of the present invention, including
the best mode thereof to one skilled in the art, is set forth more
particularly in the remainder of the specification, including reference
to the accompanying figures, in which:

[0006] FIG. 1 is a schematic view of one embodiment the laminate of the
present invention;

[0007] FIG. 2 is a schematic view of another embodiment the laminate of
the present invention; and

[0008] FIG. 3 is a schematic view of yet another embodiment the laminate
of the present invention.

DETAILED DESCRIPTION

[0009] It is to be understood that the terminology used herein is for the
purpose of describing particular embodiments only and is not intended to
limit the scope of the present invention.

[0011] "Alkenyl" refers to a linear or branched hydrocarbyl group having
from 2 to 10 carbon atoms and in some embodiments from 2 to 6 carbon
atoms or 2 to 4 carbon atoms and having at least 1 site of vinyl
unsaturation (>C.dbd.C<). For example, (C.sub.x-C.sub.y)alkenyl
refers to alkenyl groups having from x to y carbon atoms and is meant to
include for example, ethenyl, propenyl, 1,3-butadienyl, and so forth.

[0012] "Alkynyl" refers to refers to a linear or branched monovalent
hydrocarbon radical containing at least one triple bond. The term
"alkynyl" may also include those hydrocarbyl groups having other types of
bonds, such as a double bond.

[0013] "Aryl" refers to an aromatic group of from 3 to 14 carbon atoms and
no ring heteroatoms and having a single ring (e.g., phenyl) or multiple
condensed (fused) rings (e.g., naphthyl or anthryl). For multiple ring
systems, including fused, bridged, and spiro ring systems having aromatic
and non-aromatic rings that have no ring heteroatoms, the term "Aryl"
applies when the point of attachment is at an aromatic carbon atom (e.g.,
5,6,7,8 tetrahydronaphthalene-2-yl is an aryl group as its point of
attachment is at the 2-position of the aromatic phenyl ring).

[0014] "Cycloalkyl" refers to a saturated or partially saturated cyclic
group of from 3 to 14 carbon atoms and no ring heteroatoms and having a
single ring or multiple rings including fused, bridged, and spiro ring
systems. For multiple ring systems having aromatic and non-aromatic rings
that have no ring heteroatoms, the term "cycloalkyl" applies when the
point of attachment is at a non-aromatic carbon atom (e.g.,
5,6,7,8,-tetrahydronaphthalene-5-yl). The term "cycloalkyl" includes
cycloalkenyl groups, such as adamantyl, cyclopropyl, cyclobutyl,
cyclopentyl, cyclooctyl, and cyclohexenyl.

[0015] "Halo" or "halogen" refers to fluoro, chloro, bromo, and iodo.

[0016] "Haloalkyl" refers to substitution of alkyl groups with 1 to 5 or
in some embodiments 1 to 3 halo groups.

[0017] "Heteroaryl" refers to an aromatic group of from 1 to 14 carbon
atoms and 1 to 6 heteroatoms selected from oxygen, nitrogen, and sulfur
and includes single ring (e.g., imidazolyl) and multiple ring systems
(e.g., benzimidazol-2-yl and benzimidazol-6-yl). For multiple ring
systems, including fused, bridged, and spiro ring systems having aromatic
and non-aromatic rings, the term "heteroaryl" applies if there is at
least one ring heteroatom and the point of attachment is at an atom of an
aromatic ring (e.g., 1,2,3,4-tetrahydroquinolin-6-yl and
5,6,7,8-tetrahydroquinolin-3-yl). In some embodiments, the nitrogen
and/or the sulfur ring atom(s) of the heteroaryl group are optionally
oxidized to provide for the N oxide (N.fwdarw.O), sulfinyl, or sulfonyl
moieties. Examples of heteroaryl groups include, but are not limited to,
pyridyl, furanyl, thienyl, thiazolyl, isothiazolyl, triazolyl,
imidazolyl, imidazolinyl, isoxazolyl, pyrrolyl, pyrazolyl, pyridazinyl,
pyrimidinyl, purinyl, phthalazyl, naphthylpryidyl, benzofuranyl,
tetrahydrobenzofuranyl, isobenzofuranyl, benzothiazolyl,
benzoisothiazolyl, benzotriazolyl, indolyl, isoindolyl, indolizinyl,
dihydroindolyl, indazolyl, indolinyl, benzoxazolyl, quinolyl,
isoquinolyl, quinolizyl, quianazolyl, quinoxalyl, tetrahydroquinolinyl,
isoquinolyl, quinazolinonyl, benzimidazolyl, benzisoxazolyl,
benzothienyl, benzopyridazinyl, pteridinyl, carbazolyl, carbolinyl,
phenanthridinyl, acridinyl, phenanthrolinyl, phenazinyl, phenoxazinyl,
phenothiazinyl, and phthalimidyl.

[0018] "Heterocyclic" or "heterocycle" or "heterocycloalkyl" or
"heterocyclyl" refers to a saturated or partially saturated cyclic group
having from 1 to 14 carbon atoms and from 1 to 6 heteroatoms selected
from nitrogen, sulfur, or oxygen and includes single ring and multiple
ring systems including fused, bridged, and spiro ring systems. For
multiple ring systems having aromatic and/or non-aromatic rings, the
terms "heterocyclic", "heterocycle", "heterocycloalkyl", or
"heterocyclyl" apply when there is at least one ring heteroatom and the
point of attachment is at an atom of a non-aromatic ring (e.g.,
decahydroquinolin-6-yl). In some embodiments, the nitrogen and/or sulfur
atom(s) of the heterocyclic group are optionally oxidized to provide for
the N oxide, sulfinyl, sulfonyl moieties. Examples of heterocyclyl groups
include, but are not limited to, azetidinyl, tetrahydropyranyl,
piperidinyl, N-methylpiperidin-3-yl, piperazinyl,
N-methylpyrrolidin-3-yl, 3-pyrrolidinyl, 2-pyrrolidon-1-yl, morpholinyl,
thiomorpholinyl, imidazolidinyl, and pyrrolidinyl.

[0019] It should be understood that the aforementioned definitions
encompass unsubstituted groups, as well as groups substituted with one or
more other functional groups as is known in the art. For example, an
aryl, heteroaryl, cycloalkyl, or heterocyclyl group may be substituted
with from 1 to 8, in some embodiments from 1 to 5, in some embodiments
from 1 to 3, and in some embodiments, from 1 to 2 substituents selected
from alkyl, alkenyl, alkynyl, alkoxy, acyl, acylamino, acyloxy, amino,
quaternary amino, amide, imino, amidino, aminocarbonylamino,
amidinocarbonylamino, am inothiocarbonyl, aminocarbonylamino,
aminothiocarbonylamino, aminocarbonyloxy, aminosulfonyl,
aminosulfonyloxy, aminosulfonylamino, aryl, aryloxy, arylthio, azido,
carboxyl, carboxyl ester, (carboxyl ester)amino, (carboxyl ester)oxy,
cyano, cycloalkyl, cycloalkyloxy, cycloalkylthio, guanidino, halo,
haloalkyl, haloalkoxy, hydroxy, hydroxyamino, alkoxyamino, hydrazino,
heteroaryl, heteroaryloxy, heteroarylthio, heterocyclyl, heterocyclyloxy,
heterocyclylthio, nitro, oxo, oxy, thione, phosphate, phosphonate,
phosphinate, phosphonamidate, phosphorodiamidate, phosphoramidate
monoester, cyclic phosphoramidate, cyclic phosphorodiamidate,
phosphoramidate diester, sulfate, sulfonate, sulfonyl, substituted
sulfonyl, sulfonyloxy, thioacyl, thiocyanate, thiol, alkylthio, etc., as
well as combinations of such substituents. When incorporated into the
polymer of the present invention, such substitutions may be pendant or
grafted groups, or may themselves form part of the polymer backbone.

[0020] It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only, and is
not intended as limiting the broader aspects of the present invention.

[0021] Generally speaking, the present invention is directed to a laminate
for use in a printed circuit board (e.g., flexible printed circuit board)
that contains a conductive layer containing copper and a film positioned
adjacent thereto. The film is formed from a polymer composition that
contains a thermoset aromatic polyester, which includes repeating units
derived from an aromatic hydroxycarboxylic acid, aromatic
dicarboxycarboxylic acid, aromatic diol, aromatic amide, aromatic amine,
or a combination thereof. The thermoset polymer is formed by reacting an
aromatic polyester with a crosslinking agent that includes a maleimide
compound. Due to the manner in which it is formed, the film can exhibit
excellent adhesion to the conductive layer. For example, the film may
exhibit an adhesion index of about 3 or more, in some embodiments about 4
or more, and in some embodiments, from about 4.5 to 5, as determined in
accordance with ASTM D3359-09e2 (Test Method B). Due to its good adhesion
properties, the laminate may be free of an additional adhesive between
the film and the conductive layer.

[0022] Various embodiments of the present invention will now be described
in more detail.

I. Polymer Composition

[0023] A. Crosslinked Aromatic Polyester

[0024] As indicated above, the polymer composition of the present
invention includes a thermoset crosslinked aromatic polyester, which may
contain aromatic ester repeating units generally represented by the
following Formula (I):

##STR00001##

[0025] wherein,

[0026] ring B is a substituted or unsubstituted 6-membered aryl group
(e.g., 1,4-phenylene or 1,3-phenylene), a substituted or unsubstituted
6-membered aryl group fused to a substituted or unsubstituted 5- or
6-membered aryl group (e.g., 2,6-naphthalene), or a substituted or
unsubstituted 6-membered aryl group linked to a substituted or
unsubstituted 5- or 6-membered aryl group (e.g., 4,4-biphenylene); and

[0027] Y.sub.1 and Y.sub.2 are independently O, C(O), NH, C(O)HN, or
NHC(O), wherein at least one of Y.sub.1 and Y.sub.2 are C(O).

[0028] Examples of aromatic ester repeating units that are suitable for
use in the present invention may include, for instance, aromatic
dicarboxylic repeating units (Y.sub.1 and Y.sub.2 in Formula I are C(O)),
aromatic hydroxycarboxylic repeating units (Y.sub.i is 0 and Y.sub.2 is
C(O) in Formula I), as well as various combinations thereof.

[0029] Aromatic hydroxycarboxylic repeating units may, for instance, be
employed that are derived from aromatic hydroxycarboxylic acids, such as,
4-hydroxybenzoic acid; 4-hydroxy-4'-biphenylcarboxylic acid;
2-hydroxy-6-naphthoic acid; 2-hydroxy-5-naphthoic acid;
3-hydroxy-2-naphthoic acid; 2-hydroxy-3-naphthoic acid;
4'-hydroxyphenyl-4-benzoic acid; 3'-hydroxyphenyl-4-benzoic acid;
4'-hydroxyphenyl-3-benzoic acid, etc., as well as alkyl, alkoxy, aryl and
halogen substituents thereof, and combination thereof. Particularly
suitable aromatic hydroxycarboxylic acids are 6-hydroxy-2-naphthoic acid
("HNA") and 4-hydroxybenzoic acid ("HBA"). When employed, for instance,
the repeating units derived from HNA may constitute from about 15 mol. %
to about 60 mol. %, in some embodiments from about 20 mol. % to about 50
mol. %, and in some embodiments, from 30 mol. % to about 45 mol. % of the
polymer, while the repeating units derived from HBA may constitute from
about 20 mol. % to about 65 mol. %, in some embodiments from about 30
mol. % to about 60 mol. %, and in some embodiments, from about 40 mol. %
to about 55% of the polymer.

[0030] Aromatic dicarboxylic repeating units may also be employed that are
derived from aromatic dicarboxylic acids, such as terephthalic acid,
isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl
ether-4,4'-dicarboxylic acid, 1,6-naphthalenedicarboxylic acid,
2,7-naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl,
bis(4-carboxyphenyl)ether, bis(4-carboxyphenyl)butane,
bis(4-carboxyphenyl)ethane, bis(3-carboxyphenyl)ether,
bis(3-carboxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl and
halogen substituents thereof, and combinations thereof. Particularly
suitable aromatic dicarboxylic acids may include, for instance,
2,6-naphthalenedicarboxylic acid ("NDA"), terephthalic acid ("TA"), and
isophthalic acid ("IA"). When employed, for instance, repeating units
derived from NDA, IA, and/or TA may constitute from about 1 mol. % to
about 50 mol. %, in some embodiments from about 2 mol. % to about 45 mol.
%, and in some embodiments, from 5 mol. % to about 40 mol. % of the
polymer. In certain embodiments, however, the polymer may be generally
free of such dicarboxylic acid repeating units, such as about 5 mol. % or
less, and in some embodiments, about 2 mol. % or less (e.g., 0 mol. %).

[0031] Other repeating units may also be employed in the polymer. In
certain embodiments, for instance, repeating units may be employed that
are derived from aromatic diols, such as hydroquinone, resorcinol,
2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene,
1,6-dihydroxynaphthalene, 4,4'-dihydroxybiphenyl (or 4,4'-biphenol),
3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl
ether, bis(4-hydroxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl
and halogen substituents thereof, and combinations thereof. Particularly
suitable aromatic diols may include, for instance, hydroquinone ("HQ")
and 4,4'-biphenol ("BP"). When employed, repeating units derived from
aromatic diols (e.g., HQ and/or BP) typically constitute from about 1
mol. % to about 40 mol. %, in some embodiments from about 2 mol. % to
about 30 mol. %, and in some embodiments, from about 5 mol. % to about
25% of the polymer. Repeating units may also be employed, such as those
derived from aromatic amides (e.g., acetaminophen ("APAP")) and/or
aromatic amines (e.g., 4-aminophenol ("AP"), 3-aminophenol,
1,4-phenylenediamine, 1,3-phenylenediamine, etc.). When employed,
repeating units derived from aromatic amides (e.g., APAP) and/or aromatic
amines (e.g., AP) typically constitute from about 0.1 mol. % to about 20
mol. %, in some embodiments from about 0.5 mol. % to about 15 mol. %, and
in some embodiments, from about 1 mol. % to about 10% of the polymer. It
should also be understood that various other monomeric repeating units
may be incorporated into the polymer. For instance, in certain
embodiments, the polymer may contain one or more repeating units derived
from non-aromatic monomers, such as aliphatic or cycloaliphatic
hydroxycarboxylic acids, dicarboxylic acids (e.g., cyclohexane
dicarboxylic acid), diols, amides, amines, etc. Of course, in other
embodiments, the polymer may be "wholly aromatic" in that it lacks
repeating units derived from non-aromatic (e.g., aliphatic or
cycloaliphatic) monomers.

[0032] In certain embodiments of the present invention, the aromatic
polyester may be "naphthenic-rich" to the extent that it contains a high
content of repeating units derived from naphthenic hydroxycarboxylic
acids and/or naphthenic dicarboxylic acids, such as
2,6-naphthalenedicarboxylic acid ("NDA"), 6-hydroxy-2-naphthoic acid
("HNA"), or combinations thereof. That is, the total amount of repeating
units derived from naphthenic hydroxycarboxylic and/or dicarboxylic acids
(e.g., NDA, HNA, or a combination of HNA and NDA) is typically more than
about 15 mol. %, in some embodiments more than about 20 mol. %, in some
embodiments more than about 25 mol. %, and in some embodiments, from 25
mol. % to about 50 mol. % of the polymer. In one particular embodiment,
for instance, the aromatic polyester may contain repeating units derived
from HNA, HBA, BP and/or HQ, as well as various other optional
constituents. The repeating units derived from HNA may constitute from
about 15 mol. % to about 60 mol. %, in some embodiments from about 20
mol. % to about 50 mol. %, and in some embodiments, from 30 mol. % to
about 45 mol. % of the polymer. The repeating units derived from HBA may
constitute from about 20 mol. % to about 65 mol. %, in some embodiments
from about 30 mol. % to about 60 mol. %, and in some embodiments, from
about 40 mol. % to about 55% of the polymer. The repeating units derived
from BP and/or HQ may likewise constitute from about 1 mol. % to about 40
mol. %, in some embodiments from about 2 mol. % to about 30 mol. %, and
in some embodiments, from about 5 mol. % to about 25% of the polymer.

[0033] If desired, the aromatic polyester may also contain one or more
functional groups (e.g., terminal groups) that help facilitate
crosslinking. For example, the aromatic polyester may contain hydroxyl
functional groups, acyloxy functional groups, aromatic cyclic functional
groups, diene functional groups, etc. Hydroxyl functional groups may, for
instance, be introduced into the polymer through the use of a
stoichiometric excess of aromatic diols during polymerization. For
example, the ratio of the total moles of hydroxyl groups in the monomers
to the total moles of carboxyl groups in the monomers may be from about
1.01 to about 1.50, in some embodiments from about 1.05 to about 1.40,
and in some embodiments, from about 1.10 to about 1.30. In certain
embodiments, this ratio may be achieved by controlling the amount of
aromatic diol and aromatic hydroxycarboxylic acid monomers used during
polymerization. For instance, the ratio of the total moles of aromatic
diols to the total moles of aromatic hydroxycarboxylic acids may be from
about 0.10 to about 0.15, and in some embodiments, from about 0.11 to
about 0.13. Acyloxy functional groups can be introduced through the use
of acylating agents, such as acetic anhydride. Cyclic and conjugated
diene functional groups may be introduced in a similar manner. For
instance, conjugated diene functional groups may be introducing using a
conjugated diene monomer, such as 1-methyl-2,4-cyclopentadiene-1-yl)
methanol).

[0034] Regardless of its particular monomer content, the aromatic
polyester may generally be prepared by introducing the precursor monomers
into a reactor vessel to initiate a polycondensation reaction. The
particular conditions and steps employed in such reactions may be
described in more detail in U.S. Pat. No. 4,161,470 to Calundann; U.S.
Pat. No. 5,616,680 to Linstid, III, et al.; U.S. Pat. No. 6,114,492 to
Linstid, III, et al.; U.S. Pat. No. 6,514,611 to Shepherd, et al.; and WO
2004/058851 to Waggoner. The vessel employed for the reaction is not
especially limited, although it is typically desired to employ one that
is commonly used in reactions of high viscosity fluids. Examples of such
a reaction vessel may include a stirring tank-type apparatus that has an
agitator with a variably-shaped stirring blade, such as an anchor type,
multistage type, spiral-ribbon type, screw shaft type, etc., or a
modified shape thereof. Further examples of such a reaction vessel may
include a mixing apparatus commonly used in resin kneading, such as a
kneader, a roll mill, a Banbury mixer, etc.

[0035] If desired, the polymerization reaction may proceed through the
acetylation of the monomers as known in art. Acetylation may occur in a
separate reactor vessel, or it may occur in situ within the
polymerization reactor vessel. When separate reactor vessels are
employed, one or more of the monomers may be introduced to the
acetylation reactor and subsequently transferred to the melt
polymerization reactor. Likewise, one or more of the monomers may also be
directly introduced to the reactor vessel without undergoing
pre-acetylation. Acetylation may be accomplished by adding an acetylating
agent (e.g., acetic anhydride) to one or more of the monomers. One
particularly suitable technique for acetylating monomers may include, for
instance, charging precursor monomers (e.g., HNA, HBA, BP, and/or HQ) and
acetic anhydride into a reactor and heating the mixture to acetylize a
hydroxyl group of the monomers (e.g., forming acetoxy).

[0036] Acetylation is generally initiated at temperatures of about
90.degree. C. During the initial stage of the acetylation, reflux may be
employed to maintain vapor phase temperature below the point at which
acetic acid byproduct and anhydride begin to distill. Temperatures during
acetylation typically range from between 90.degree. C. to 150.degree. C.,
and in some embodiments, from about 110.degree. C. to about 150.degree.
C. If reflux is used, the vapor phase temperature typically exceeds the
boiling point of acetic acid, but remains low enough to retain residual
acetic anhydride. For example, acetic anhydride vaporizes at temperatures
of about 140.degree. C. Thus, providing the reactor with a vapor phase
reflux at a temperature of from about 110.degree. C. to about 130.degree.
C. is particularly desirable. To ensure substantially complete reaction,
an excess amount of acetic anhydride may be employed. The amount of
excess anhydride will vary depending upon the particular acetylation
conditions employed, including the presence or absence of reflux. The use
of an excess of from about 1 to about 10 mole percent of acetic
anhydride, based on the total moles of reactant hydroxyl groups present
is not uncommon.

[0037] After any optional acetylation is complete, the resulting
composition may be melt-polymerized. Although not required, this is
typically accomplished by transferring the acetylated monomer(s) to a
separator reactor vessel for conducting a polycondensation reaction. If
desired, one or more of the precursor monomers used to form the aromatic
polyester may be directly introduced to the melt polymerization reactor
vessel without undergoing pre-acetylation. Other components may also be
included within the reaction mixture to help facilitate polymerization.
For instance, a catalyst may be optionally employed, such as metal salt
catalysts (e.g., magnesium acetate, tin(I) acetate, tetrabutyl titanate,
lead acetate, sodium acetate, potassium acetate, etc.) and organic
compound catalysts (e.g., N-methylimidazole). Such catalysts are
typically used in amounts of from about 50 to about 500 parts per million
based on the total weight of the recurring unit precursors. The catalyst
is typically added to the acetylation reactor rather than the
polymerization reactor, although this is by no means a requirement.

[0038] In some embodiments, the melt polymerized polymer may also be
subjected to a subsequent solid-state polymerization method to further
increase its molecular weight. For instance, solid-state polymerization
may be conducted in the presence of a gas (e.g., air, inert gas, etc.).
Suitable inert gases may include, for instance, include nitrogen, helium,
argon, neon, krypton, xenon, etc., as well as combinations thereof. The
solid-state polymerization reactor vessel can be of virtually any design
that will allow the polymer to be maintained at the desired solid-state
polymerization temperature for the desired residence time. Examples of
such vessels can be those that have a fixed bed, static bed, moving bed,
fluidized bed, etc. The temperature at which solid-state polymerization
is performed may vary, but is typically within a range of from about
250.degree. C. to about 300.degree. C. The polymerization time will of
course vary based on the temperature and target molecular weight. In most
cases, however, the solid-state polymerization time will be from about 2
to about 12 hours, and in some embodiments, from about 4 to about 10
hours.

[0039] As indicated above, a crosslinking agent is reacted with the
aromatic polyester after it is formed to form the thermoset polymer. The
crosslinking agent includes a maleimide compound, which may contain a
functional group that is reactive with a functional group present on the
aromatic polyester (e.g., hydroxyl, acyloxy, conjugated diene, etc.). If
desired, this reaction may occur in the presence of an organic solvent,
such as glycols (e.g., propylene glycol, butylene glycol, triethylene
glycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, and
dipropyleneglycol); alcohols (e.g., methanol, ethanol, n-propanol, and
isopropanol); triglycerides; ethyl acetate; acetone; triacetin;
acetonitrile, tetrahydrafuran; xylenes; formaldehydes (e.g.,
dimethylformamide, "DMF"); etc. In such embodiments, the reaction of the
aromatic polyester and the crosslinking agent may occur at a relatively
low temperature, such as from about 100.degree. C. to about 250.degree.
C., in some embodiments from about 110.degree. C. to about 200.degree.
C., and in some embodiments, from about 120.degree. C. to about
180.degree. C. Of course, other techniques may also be employed to induce
the desired crosslinking reaction. For example, melt blending techniques
may be employed in which the crosslinking agent is blended and reacted
with the aromatic polyester while it is in a melt phase (e.g., within an
extruder). In such embodiments, the reaction of the aromatic polyester
and the crosslinking agent may occur at a temperature of from about
200.degree. C. to about 450.degree. C., in some embodiments from about
250.degree. C. to about 400.degree. C., and in some embodiments, from
about 275.degree. C. to about 350.degree. C. Regardless of the particular
method employed, the relative amount of the crosslinking agent may be
from about 0.01 to about 10 parts, in some embodiments from about 0.05 to
about 8 parts, and in some embodiments, from about 0.1 to about 5 parts
by weight relative to 100 parts by weight of the aromatic polyester. The
crosslinking agents may, for example, constitute from about 0.01 wt. % to
about 10 wt. %, in some embodiments from about 0.05 wt. % to about 8 wt.
%, and in some embodiments, from about 0.1 wt. % to about 5 wt. % of the
reaction mixture. Aromatic polyesters may likewise constitute from about
90 wt. % to about 99.99 wt. %, in some embodiments from about 92 wt. % to
about 99.95 wt. %, and in some embodiments, from about 95 wt. % to about
99.9 wt. % of the reaction mixture.

[0040] Typically, the maleimide compound used for the crosslinking agent
has relatively low molecular weight so that it does not adversely impact
the melt rheology of the resulting polymer. For example, the compound
typically has a molecular weight of about 3,000 grams per mole or less,
in some embodiments from about 20 to about 2,000 grams per mole, in some
embodiments from about 30 to about 1,000 grams per mole, and in some
embodiments, from about 50 to about 500 grams per mole. The melting
temperature of the maleimide compound may also be relatively low, such as
about 150.degree. C. or less, in some embodiments from about 20.degree.
C. to about 130.degree. C., and in some embodiments, from about
30.degree. C. to about 100.degree. C.

[0041] In certain cases, for instance, the maleimide compound may be a
bismaleimide having the following general formula:

[0043] In certain embodiments, for instance, R.sup.1 may be an aryl group
that contains one or more aromatic rings having from 6 to 15 carbon
atoms, and in some embodiments, from 6 to 10 carbon atoms (e.g., phenyl).
The aryl group may generally contain any number of aromatic rings
desired. For instance, in one embodiment, a single aromatic ring may be
employed. Likewise, in other embodiments, multiple aromatic rings may be
employed, such as from 2 to 6, and in some embodiments, from 2 to 4. If
desired, one or more linking groups may also be employed between adjacent
aromatic rings and/or between an aromatic ring and the nitrogen atom of
the imide group. Examples of such linking groups may include, for
instance, ether (--O--), thioether (--S--), acyl (--C(O)--), ester
(--C(O)O--), sulfonyl (--SO.sub.2--), alkyl (e.g., --CH.sub.2--), alkoxy
(e.g., --OCH.sub.2--, --OCH.sub.2CH.sub.2--O--, etc.), amide (--NHCO--),
etc.

[0044] Particularly suitable bismaleimides are those in which the aryl
group of R.sup.1 contains two aromatic rings (e.g., phenyl). Examples of
such biaromatic bismaleimides include, for instance,
4,4'-dimaleimidophenylmethane (diphenylmethane bismaleimide),
N,N'-(3,3'-dimethyl-4,4'-biphenylylene) bismaleimide,
3,3'-dichloro-4,4'-diphenylmethane bismaleimide, 3,3'-dimethyl-4,4'
diphenylmethane bismaleimide, 3,3'-dimethoxy-4,4'-diphenylmethane
bismaleimide, 4,4'-diphenylsulfide bismaleimide, 4,4'-diphenylether
bismaleimide, 3,3'-benzophenone bismaleimide, 3,
3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, etc. Yet
other suitable bismaleimides may also be employed. For instance, some
examples of suitable bismaleimides in which the aryl group of R.sup.1
contains only one aromatic ring (e.g., phenyl) include
4-methyl-1,3-phenylene bismaleimide, 1, 3-phenylene bismaleimide,
1,4-phenylene bismaleimide, 1,2-phenylene bismaleimide,
naphthalene-1,5-bismaleimide, 4-chloro-1,3-phenylene bismaleimide, etc.
Likewise, some examples of suitable bismaleimides in which the aryl group
of R.sup.1 contains three or more aromatic rings (e.g., phenyl) include
2,2-bis [4-(4-maleimide phenoxy)phenyl]propane,
bis[4-maleimide(4-phenoxyphenyl)sulfone, 1,3-bis(4-maleimide
phenoxy)benzene, 1,3-bis(3-maleimide phenoxy)benzene, etc.

[0047] The aromatic polyester of the present invention may be used alone
or in combination with various other optional additives to form the
polymer composition, such as other thermoset resins, inorganic fillers,
flame retardants, viscosity modifiers, antimicrobials, pigments,
antioxidants, stabilizers, surfactants, waxes, flow promoters, solid
solvents, and other materials added to enhance properties and
processibility. For instance, the polymer composition may contain another
type of thermoset resin to help improve the insulating and adhesive
properties of the composition. Examples of such resins may include, for
instance, epoxy resins, acrylates, cyano-acrylates, cyano-esters,
urethanes, etc. One particular example of such a resin is an epoxy resin,
which typically contains an epoxide and a curing agent. The epoxide may
include an organic compound having at least one oxirane ring
polymerizable by a ring opening reaction, and can be aliphatic,
heterocyclic, cycloaliphatic, and/or aromatic. The epoxide may be a
"polyepoxide" in that it contains at least two epoxy groups per molecule,
and it may be monomeric, dimeric, oligomeric or polymeric in nature. The
backbone of the resin may be of any type, and substituent groups thereon
can be any group not having a nucleophilic group or electrophilic group
(such as an active hydrogen atom) which is reactive with an oxirane ring.
Exemplary substituent groups include halogens, ester groups, ethers,
sulfonate groups, siloxane groups, nitro groups, amide groups, nitrile
groups, and phosphate groups.

[0048] Suitable epoxide resins may include, for instance, the reaction
product of bisphenol A and epichlorohydrin, the reaction product of
phenol and formaldehyde (novolac resin) and epichlorohydrin, peracid
epoxies, glycidyl esters, glycidyl ethers, the reaction product of
epichlorohydrin and p-amino phenol, the reaction product of
epichlorohydrin and glyoxal tetraphenol, etc. Particularly suitable
epoxides have the general structure set forth below in general formula
(I):

##STR00003##

[0049] wherein n is 1 or more, and in some embodiments, from 1 to 4, and
R' is an organic residue that may include, for example, an alkyl group,
an alkyl ether group, or an aryl group; and n is at least 1. For example,
R' may be a poly(alkylene oxide). Suitable glycidyl ether epoxides of
formula (I) include glycidyl ethers of bisphenol A and F, aliphatic diols
or cycloaliphatic diols. The glycidyl ether epoxides may include linear
polymeric epoxides having terminal epoxy groups (e.g., a diglycidyl ether
of polyoxyalkylene glycol) and aromatic glycidyl ethers (e.g., those
prepared by reacting a dihydric phenol with an excess of
epichlorohydrin). Examples of dihydric phenols include resorcinol,
catechol, hydroquinone, and the polynuclear phenols including
p,p'-dihydroxydibenzyl, p,p'-dihydroxyphenylsulfone,
p,p'-dihydroxybenzophenone, 2,2'-dihydroxyphenyl sulfone,
p,p'-dihydroxybenzophenone, 2,2-dihydroxy-1,1-dinaphrhylmethane, and the
2,2', 2,3', 2,4', 3,3', 3,4', and 4,4' isomers of
dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane,
dihydroxydiphenylethylmethylmethane,
dihydroxydiphenylmethylpropylmethane,
dihydroxydiphenylethylphenylmethane,
dihydroxydiphenylpropylenphenylmethane,
dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane,
dihydroxydiphenyltolylmethylmethane,
dihydroxydiphenyldicyclohexylmethane, and dihydroxydiphenylcyclohexane.

[0050] The epoxy resin may also include a curing agent capable of
cross-linking the epoxide, such as room temperature curing agents,
heat-activated curing agents, etc. Examples of such curing agents may
include, for instance, imidazoles, imidazole-salts, imidazolines,
tertiary amine, and/or primary or secondary amines, such as diamine,
diethylene diamine, diethylene triamine, triethylene tetramine, propylene
diamine, tetraethylene pentamine, hexaethylene heptamine, hexamethylene
diamine, 2-methyl-1,5-pentamethylene-diamine,
4,7,10-trioxatridecan-1,13-diamine, aminoethylpiperazine, etc. In certain
embodiments, the curing agent is a polyether amine having one or more
amine moieties, including those polyether amines that can be derived from
polypropylene oxide or polyethylene oxide.

[0051] When employed, additional thermoset resins may constitute from
about 10 to about 90 wt. %, in some embodiments from about 20 wt. % to
about 85 wt. %, and in some embodiments, from about 30 wt. % to about 80
wt. % of the polymer composition. Nevertheless, one beneficial aspect of
the present invention is that good properties may be achieved without the
need for various conventional thermoset resins, such as epoxy resins. In
fact, in certain embodiments of the present invention, the polymer
composition may be generally free of epoxy resins and/or other
conventional thermoset resins. For example, in such embodiments,
additional thermoset resins (e.g., epoxy resins) may be present in an
amount of no more than about 5 wt. %, in some embodiments no more than
about 1 wt. %, and in some embodiments, from about 0.001 wt. % to about
0.5 wt. % of the polymer composition.

[0052] An inorganic filler may also be employed in the polymer composition
to help improve the dimensional stability and mechanical strength of the
polymer composition. Examples of suitable inorganic fillers include, for
instance, silica (fused, non-fused, porous, or hollow), aluminum oxide,
aluminum hydroxide, magnesium oxide, magnesium hydroxide, calcium
carbonate, aluminum nitride, boron nitride, aluminum silicon carbide,
silicon carbide, sodium carbonate, titanium dioxide, zinc oxide,
zirconium oxide, quartz, diamond powder, diamond-like powder, graphite,
magnesium carbonate, potassium titanate, mica, boehmite, zinc molybdate,
ammonium molybdate, zinc borate, calcium phosphate, talc, talc, silicon
nitride, mullite, kaolin, clay, etc. Silica and alumina nitride may be
particularly suitable for use in the polymer composition. When employed,
inorganic fillers may constitute from about 0.5 to about 40 wt. %, in
some embodiments from about 1 wt. % to about 35 wt. %, and in some
embodiments, from about 5 wt. % to about 30 wt. % of the polymer
composition. Nevertheless, one beneficial aspect of the present invention
is that good dimensional stability may be achieved without the need for
various conventional inorganic fillers, such as silica or aluminum
nitride. In fact, in certain embodiments of the present invention, the
polymer composition may be generally free of silica and/or other
conventional inorganic fillers. For example, in such embodiments,
inorganic fillers (e.g., silica, aluminum nitride, etc.) may be present
in an amount of no more than about 0.5 wt. %, in some embodiments no more
than about 0.1 wt. %, and in some embodiments, from about 0.001 wt. % to
about 0.1 wt. % of the polymer composition.

[0053] In certain embodiments, it may be desired that the polymer
composition is generally fire resistant. In this regard, a
flame-retardant may optionally be employed in the polymer composition.
Flame retardants that have a low content of halogens (e.g., bromine,
chlorine, and/or fluorine) are particularly suitable for use in the
present invention. For example, the flame retardants, as well as the
resulting polymer composition, may have a halogen content of about 500
parts per million by weight ("ppm") or less, in some embodiments about
100 ppm or less, and in some embodiments, about 50 ppm or less. In
certain embodiments, the flame retardants are free of halogens (i.e.,
"halogen free").

[0054] One example of a suitable flame retardant, for instance, is an
organophosphorous compound, such as a salt of phosphinic acid and/or
diphosphinic acid (i.e., "phosphinate") having the general formula (IV)
and/or formula (V):

[0059] m is from 1 to 4, in some embodiments from 1 to 3, and in some
embodiments, from 2 to 3 (e.g., 3);

[0060] n is from 1 to 4, in some embodiments from 1 to 3, and in some
embodiments, from 2 to 3 (e.g., 3);

[0061] p is from 1 to 4, in some embodiments from 1 to 3, and in some
embodiments, from 1 to 2; and

[0062] y is from 1 to 4, in some embodiments from 1 to 3, and in some
embodiments, from 1 to 2.

[0063] The phosphinates may, for instance, be prepared using any known
technique, such as by reacting a phosphinic acid with metal carbonates,
metal hydroxides or metal oxides in aqueous solution. Suitable
phosphinates include, for example, salts (e.g., aluminum or calcium salt)
of dimethylphosphinic acid, ethylmethylphosphinic acid, diethylphosphinic
acid, methyl-n-propylphosphinic acid, methane-di(methylphosphinic acid),
ethane-1,2-di(methylphosphinic acid), hexane-1,6-di(methylphosphinic
acid), benzene-1,4-di(methylphosphinic acid), methylphenylphosphinic
acid, diphenylphosphinic acid, hypophosphoric acid, etc. The resulting
salts are typically monomeric compounds; however, polymeric phosphinates
may also be formed. Additional examples of suitable phosphinic compounds
and their methods of preparation are described in U.S. Pat. No. 7,087,666
to Hoerold, et al.; U.S. Pat. No. 6,716,899 to Klatt, et al.; U.S. Pat.
No. 6,270,500 to Kleiner, et al.; U.S. Pat. No. 6,194,605 to Kleiner;
U.S. Pat. No. 6,096,914 to Seitz; and U.S. Pat. No. 6,013,707 to Kleiner,
et al.

[0064] Another suitable halogen-free organophosphorous flame retardant may
be a polyphosphate having the following general formula:

##STR00005##

[0065] v is from 1 to 1000, in some embodiments from 2 to 500, in some
embodiments from 3 to 100, and in some embodiments, from 5 to 50; and

[0066] Q is a nitrogen base. Suitable nitrogen bases may include those
having a substituted or unsubstituted ring structure, along with at least
one nitrogen heteroatom in the ring structure (e.g., heterocyclic or
heteroaryl group) and/or at least one nitrogen-containing functional
group (e.g., amino, acylamino, etc.) substituted at a carbon atom and/or
a heteroatom of the ring structure. Examples of such heterocyclic groups
may include, for instance, pyrrolidine, imidazoline, pyrazolidine,
oxazolidine, isoxazolidine, thiazolidine, isothiazolidine, piperidine,
piperazine, thiomorpholine, etc. Likewise, examples of heteroaryl groups
may include, for instance, pyrrole, imidazole, pyrazole, oxazole,
isoxazole, thiazole, isothiazole, triazole, furazan, oxadiazole,
tetrazole, pyridine, diazine, oxazine, triazine, tetrazine, and so forth.
If desired, the ring structure of the base may also be substituted with
one or more functional groups, such as acyl, acyloxy, acylamino, alkoxy,
alkenyl, alkyl, amino, aryl, aryloxy, carboxyl, carboxyl ester,
cycloalkyl, hydroxyl, halo, haloalkyl, heteroaryl, heterocyclyl, etc.
Substitution may occur at a heteroatom and/or a carbon atom of the ring
structure. For instance, one suitable nitrogen base may be a triazine in
which one or more of the carbon atoms in the ring structure are
substituted by an amino group. One particularly suitable base is
melamine, which contains three carbon atoms in the ring structure
substituted with an amino functional group.

[0067] The amount of the aromatic polyester employed in forming the
polymer composition may vary widely depending on the particular nature of
the additives selected. In certain embodiments, for example, the aromatic
polyester may form a substantial portion of the composition and serve as
a major resinous component. In such cases, the aromatic polyester may,
for instance, constitute from about 40 wt. % to about 95 wt. %, in some
embodiments from about 50 wt. % to about 90 wt. %, and in some
embodiments, from about 60 wt. % to about 85 wt. % of the composition. In
yet other embodiments, however, the aromatic polyester may simply be used
as a filler. In such cases, the aromatic polyester may constitute from
about 0.5 to about 40 wt. %, in some embodiments from about 1 wt. % to
about 35 wt. %, and in some embodiments, from about 5 wt. % to about 30
wt. % of the polymer composition.

[0068] Regardless of the manner in which it is formed, the thermoset
aromatic polyester and polymer composition may exhibit excellent thermal
properties. For example, the polyester and/or polymer composition may
have a relatively high melting temperature. The melting temperature may,
for example, range from about 200.degree. C. to about 370.degree. C., in
embodiments from about 250.degree. C. to about 360.degree. C., in some
embodiments from about 280.degree. C. to about 350.degree. C., in some
embodiments from about 290.degree. C. to about 335.degree. C., and in
some embodiments, from about 300.degree. C. to about 330.degree. C., such
as determined by differential scanning calorimetry in accordance with ISO
Test No. 11357-2:2013. While having a relatively high melting
temperature, the polyester and/or polymer composition may nevertheless
maintain a relatively low melt viscosity, such as about 150 Pa-s or less,
in some embodiments about 100 Pa-s or less, in some embodiments from
about 1 to about 80 Pa-s, and in some embodiments, from about 2 to about
50 Pa-s. Melt viscosity may be determined in accordance with ISO Test No.
11443:2005 at a shear rate of 1000 s.sup.-1 and using a Dynisco LCR7001
capillary rheometer. The melt viscosity is also typically determined at a
temperature at least 15.degree. C. above the melting temperature (e.g.,
300.degree. C., 320.degree. C., or 350.degree. C.). As a result of such
properties, the polymer composition is capable of exhibiting good thermal
properties while remaining relatively flowable and easy to process, which
can provide a great degree of flexibility in the particular type of
application method that is employed.

II. Film

[0069] Any of variety of different techniques may generally be used to
form the polymer composition into a film. Suitable techniques may
include, for instance, solvent casting, melt extrusion (e.g., die
casting, blown film casting, extrusion coating, etc.), and so forth. In
one particular embodiment, a blown film process is employed in which the
composition is fed to an extruder, where it is melt processed and then
supplied through a blown film die to form a molten bubble. Typically, the
die contains a mandrel that is positioned within the interior of an outer
die body so that a space is defined therebetween. The polymer composition
is blown through this space to form the bubble, which can then be drawn,
inflated with air, and rapidly cooled so that the polymer composition
quickly solidifies. If desired, the bubble may then be collapsed between
rollers and optionally wound onto a reel.

[0070] The thickness of the film may vary, but is typically about 500
micrometers or less, in some embodiments from about 1 to about 250
micrometers, in some embodiments from about 2 to about 100 micrometers,
and in some embodiments, from about 5 to about 50 micrometers. The film
may be generally impervious to gases and moisture due to the presence of
the polymer composition. For example, the film may be impervious to gases
in that it prevents the mass transfer of gases at typical atmospheric
conditions, such as oxygen, carbon dioxide or nitrogen. Oxygen barrier
properties, for instance, are typically measured in g/m.sup.2-24 hr. In
the present invention, the film may have an oxygen transmission rate of
about 0.3 g/m.sup.2-24 hr or less, in some embodiments about 0.2
g/m.sup.2-24 hr or less, and in some embodiments, about 0.1 g/m.sup.2-24
hr or less, as determined in accordance with ASTM D3985-05 at a
temperature of 23.degree. C. and a relative humidity of 0%. The
resistance to the mass transfer of liquid vapors at a certain partial
pressure and temperature across a material can be expressed as the
moisture vapor transmission rate with the units of g/m.sup.2-24 hr. The
film may have a moisture vapor transmission rate of about 0.2
g/m.sup.2-24 hr or less, in some embodiments about 0.1 g g/m.sup.2-24 hr
or less, and in some embodiments, about 0.05 g/m.sup.2-24 hr or less,
determined in accordance with ASTM F1249-06 at a temperature of
100.degree. F. and 90% relative humidity.

[0071] The film may also exhibit relatively high peak elongation values in
the machine and/or cross-machine direction, such as about 5% or more, in
some embodiments about 10% or more, and in some embodiments, from about
15% to about 50%. In addition, the film may exhibit a Young's modulus of
elasticity in the machine direction and/or cross-machine direction of
from about 500 to about 10,000 MPa, in some embodiments from about 1,000
to about 6,000 MPa, and in some embodiments, from about 1,500 to about
3,000 MPa. Despite having good modulus and elongation values, the film of
the present invention is nevertheless able to retain good mechanical
strength. For example, the film of the present invention may exhibit a
tensile strength (stress) in the machine direction and/or cross-machine
direction of from about 15 to about 300 Megapascals (MPa), in some
embodiments from about 30 to about 200 MPa, and in some embodiments, from
about 50 to about 150 MPa. Surprisingly, such good properties can be
achieved even though the film has a very low thickness. The tensile
properties (e.g., Young's modulus of elasticity, peak elongation, and
tensile strength) may be tested according to ASTM D882-12. Measurements
may be made on a test strip sample having a gage length of 25.4 mm,
thickness of 25 um, and width of 6.35 mm. The testing temperature may be
23.degree. C., and the testing speed may be 2.54 mm/min.

[0072] Further, the film may exhibit good electrical properties. For
instance, the film may have a relatively low dielectric constant that
allows it to be employed as a heat dissipating material in various
electronic applications (e.g., flexible printed circuit boards). For
example, the average dielectric constant may be about 5.0 or less, in
some embodiments from about 0.1 to about 4.5, and in some embodiments,
from about 0.2 to about 3.5, as determined by the split post resonator
method at a variety of frequencies, such as from about 1 to about 15 GHz
(e.g., 1, 2, or 10 GHz). The dissipation factor, a measure of the loss
rate of energy, may also be relatively low, such as about 0.0060 or less,
in some embodiments about 0.0050 or less, and in some embodiments, from
about 0.0010 to about 0.0040, as determined by the split post resonator
method at a variety of frequencies, such as from about 1 to about 15 GHz
(e.g., 1, 2, or 10 GHz).

II. Conductive Layer

[0073] As noted above, the film is positioned adjacent to at least one
conductive layer to form the laminate of the present invention. The
conductive layer may be provided in a variety of different forms, such as
membranes, films, molds, wafers, tubes, etc. For example, the layer may
have a foil-like structure in that it is relatively thin, such as having
a thickness of about 500 micrometers or less, in some embodiments about
200 micrometers or less, and in some embodiments, from about 1 to about
100 micrometers. Of course, higher thicknesses may also be employed. The
conductive layer also contains copper (e.g., pure copper and copper
alloys). If desired, the conductive layer may also contain other
conductive materials, such as other metals (e.g., gold, silver, nickel,
aluminum, etc.).

[0074] The film may be applied to the conductive layer using techniques
such as described above (e.g., casting), or the conductive layer may
alternatively be applied to the film using techniques such as ion beam
sputtering, high frequency sputtering, direct current magnetron
sputtering, glow discharge, etc. If desired, the film may be subjected to
a surface treatment on a side facing the conductive layer so that the
adhesiveness between the film and conductive layer is improved. Examples
of such surface treatments include, for instance, corona discharge
treatment, UV irradiation treatment, plasma treatment, etc. When applied
to a conductive layer, the film may be optionally annealed to improve its
properties. For example, annealing may occur at a temperature of from
about 250.degree. C. to about 400.degree. C., in some embodiments from
about 260.degree. C. to about 350.degree. C., and in some embodiments,
from about 280.degree. C. to about 330.degree. C., and for a time period
ranging from about 15 minutes to about 300 minutes, in some embodiments
from about 20 minutes to about 200 minutes, and in some embodiments, from
about 30 minutes to about 120 minutes. During annealing, it is sometimes
desirable to restrain the film at one or more locations (e.g., edges) so
that it is not generally capable of physical movement. This may be
accomplished in a variety of ways, such as by clamping, taping, or
otherwise adhering the film to the conductive layer.

[0075] The laminate may have a two-layer structure containing only the
film and conductive layer. Referring to FIG. 1, for example, one
embodiment of such a two layer structure 10 is shown as containing a film
11 positioned adjacent to a conductive layer 12 (e.g., copper foil).
Alternatively, a multi-layered laminate may be formed that contains two
or more conductive layers and/or two or more films. Referring to FIG. 2,
for example, one embodiment of a three-layer laminate structure 100 is
shown that contains a film 110 positioned between two conductive layers
112. Yet another embodiment is shown in FIG. 3. In this embodiment, a
seven-layered laminate structure 200 is shown that contains a core 201
formed from a film 210 positioned between two conductive layers 212.
Films 220 likewise overlie each of the conductive layers 212,
respectively, and external conductive layers 222 overlie the films 220.
In the embodiments described above, the film of the present invention may
be used to form any, or even all of the film layers. Various conventional
processing steps may be employed to provide the laminate with sufficient
strength. For example, the laminate may be pressed and/or subjected to
heat treatment as is known in the art.

[0077] These and other modifications and variations of the present
invention may be practiced by those of ordinary skill in the art, without
departing from the spirit and scope of the present invention. In
addition, it should be understood that aspects of the various embodiments
may be interchanged both in whole or in part. Furthermore, those of
ordinary skill in the art will appreciate that the foregoing description
is by way of example only, and is not intended to limit the invention so
further described in such appended claims.